This invention relates to millimeter waveguides, and, more particularly, to a gasket placed between two millimeter waveguide sections joined end to end.
Millimeter waves are electromagnetic waves having very short wavelengths, about 1 centimeter or less in wavelength, that transmit radio frequency energy. Millimeter waves are used in a variety of applications, including communications, where they can carry large amounts of information. Like radio waves, millimeter waves can either be beamed from place to place, or carried along a conductive path.
The conductive path used to carry millimeter waves is usually a waveguide. A conventional waveguide is a tube whose inside surface is coated with a conductive metal such as gold or silver. The microwaves travel along the inside of the tubular waveguide, which is usually cylindrical or rectangular in shape.
Waveguides are generally formed in sections for convenience or because of manufacturing or technical constraints. The sections must be joined together end-to-end when the final waveguide is assembled. To facilitate the joining, the waveguides are provided with flanges at the ends, and the flanges are bolted together.
A significant amount of the transmitted radio frequency energy can leak from unprotected joints between waveguide sections, particularly where the microwaves are of very short wavelengths on the order of 1 millimeter or less. When the waveguide is formed of a number of individual sections joined together, the loss of energy from the waveguide joints can be significant. The leakage of radio frequency energy interferes with, even to the point of overpowering, neighboring electronic devices (hence the leakage is termed EMI, or electromagnetic interference), and also cumulatively reduces the transmitted energy level. It is important to minimize the leakage at each joint between sections.
The prevention of leakage of radio frequency energy from the joints between millimeter waveguide sections is significantly more difficult than the corresponding problem for microwave waveguides, which have longer wavelengths of greater than 1 centimeter. The use of machining tolerances on the order of 0.001 inch on the flange faces, microwave gaskets, and choke flanges prevents leakage from microwave waveguide joints. These techniques have proved ineffective in preventing leakage from joints in millimeter waveguides, which are smaller in size than microwave waveguides. Because millimeter waves have shorter wavelengths, even tiny imperfections in the flanges and slight misalignments between waveguide sections can result in significant leakage of radio frequency energy. The prevention of energy loss from the joints between millimeter waveguide sections is recognized as a qualitatively different problem from that of prevention of energy loss from the joints between microwave sections.
There have been proposed several approaches for preventing leakage from the joints between millimeter waveguide sections. In one, a silver filled epoxy is forced into the joints and permitted to harden in place. This approach has the significant disadvantage of preventing easy disassembly of the sections and also contaminates the interior of the waveguide sections. In another approach, the gap between the waveguide sections is wrapped with a copper tape or foil that inhibits leakage. This method requires skilled technicians, is time consuming, requires specialized test equipment, is cumbersome, and is sometimes completely impractical, as where a waveguide section flange is joined to a flat surface.
It has also been proposed to use a hard gasket filled with conductive particles, which is placed between the flanges of the waveguide sections before bolting. Such gaskets have been used successfully between microwave waveguide sections, but are insufficiently effective in reducing energy leakage for short wavelength, high frequency millimeter waves.
There therefore exists a need for an improved approach for reducing leakage at the joint between millimeter waveguide sections that are joined end to end. The approach should be convenient and inexpensive to use, and should be effective in preventing leakage from the flanged joints of millimeter waveguides. The present invention fulfills this need, and further provides related advantages.